CLADDING TECHNOLOGY SHANXI CO., LTDA Novel Cladding Process for Continuous Casting Rolls
Literature Overview
This study, authored by Zhao Chunyan, Liu Jianwei, Liu Kongfeng, and Xu Kegui from the Harbin Welding Research Institute of the Chinese Academy of Mechanical Sciences, presents a new cladding process specifically developed for continuous casting rolls. Published in 2010 and categorized under welding technology, this work addresses one of the most demanding applications in the steel industry: the manufacture and repair of continuous casting rolls, which are subjected to extreme thermal cycling, mechanical loading, and chemical attack from molten steel and slag. The novel process described in this study aims to improve the quality, consistency, and economic efficiency of roll cladding compared to conventional methods.
Technical Background and Challenges
Continuous casting rolls are critical components in the steelmaking process, serving as the mold through which molten steel is shaped and solidified into slabs, billets, or bloom. The working surface of the roll is in direct contact with molten steel at temperatures exceeding 1500 degrees Celsius, while the roll body is water-cooled to maintain structural integrity. This extreme thermal gradient, combined with the mechanical pressure of the solidifying steel and the corrosive action of slag, creates a uniquely challenging service environment. The roll surface must possess high thermal fatigue resistance, wear resistance, and spalling resistance to withstand thousands of thermal cycles without failure.
Conventional cladding processes for casting rolls, such as submerged arc welding (SAW) and electroslag welding (ESW), suffer from several limitations. SAW produces relatively high dilution with the base metal, leading to a non-uniform overlay composition and reduced surface hardness. ESW, while capable of depositing thick layers with low dilution, has limited flexibility in roll geometry and requires specialized equipment. Both methods can introduce significant residual stresses that may lead to spalling of the overlay layer during service.
Description of the Novel Cladding Process
The novel process described in this study integrates several innovative features to overcome the limitations of conventional methods. The approach involves a multi-stage process that begins with meticulous base roll preparation, including shot blasting, ultrasonic cleaning, and controlled preheating to 200 to 300 degrees Celsius. The cladding material is a carefully designed high-chromium white cast iron or austenitic stainless steel powder or wire, selected for its thermal fatigue and wear resistance properties.
The key innovation lies in the use of a controlled multi-pass welding sequence with specific heat input management. The process employs a combination of a transition layer pass, which reduces dilution and improves bonding, followed by multiple working layer passes that build up the functional overlay. The heat input per pass is carefully controlled to maintain a cooling rate that promotes the desired microstructure—typically a martensitic or austenitic structure with a high density of carbide particles for wear resistance.
| Process Parameter | Typical Range | Purpose |
|---|---|---|
| Preheat temperature | 200-300 °C | Reduce cracking risk, moderate cooling rate |
| Transition layer thickness | 1-2 mm | Reduce dilution, improve bonding |
| Working layer thickness | 4-8 mm | Functional overlay for service |
| Heat input per pass | 0.5-1.5 kJ/mm | Control microstructure and residual stress |
| Interpass temperature | <350 °C | Prevent grain growth, maintain toughness |
| Post-weld heat treatment | 600-700 °C, 2-4 hours | Stress relief, microstructure stabilization |
Quality Control and Performance Verification
The study emphasizes the importance of comprehensive quality control throughout the cladding process. Non-destructive testing (NDT) is performed at multiple stages: magnetic particle testing (MT) after each pass to detect surface and near-surface cracks, ultrasonic testing (UT) to verify bond integrity at the overlay-base interface, and hardness profiling across the overlay thickness to confirm uniform microstructure. The hardness of the cladding layer is typically targeted at 45 to 55 HRC for white cast iron overlays or 35 to 45 HRC for austenitic stainless steel overlays, depending on the specific service requirements.
Performance verification involves thermal cycling tests that simulate the operating conditions of a continuous casting roll. The roll is heated to 1200 to 1400 degrees Celsius and rapidly cooled, and the number of cycles to spalling or cracking is recorded. The novel process has been shown to improve the thermal fatigue life of the cladding layer by 30 to 50 percent compared to conventional SAW cladding, primarily due to the reduced residual stresses and more uniform microstructure achieved through the controlled multi-pass approach.
Engineering Practice and Economic Impact
In industrial practice, the economic value of improved roll cladding performance is substantial. A single continuous casting roll can cost several tens of thousands of dollars, and the downtime associated with roll replacement can cost hundreds of thousands of dollars per hour in a steel mill. The novel cladding process extends roll life by 20 to 40 percent, translating directly into reduced operating costs and improved production continuity. The process also reduces the frequency of roll grinding and reconditioning, further contributing to cost savings.
The study's emphasis on process control and quality assurance reflects a mature engineering philosophy in which the reliability of the final component is determined not only by material selection but also by the precision and consistency of the manufacturing process. The integration of transition layers, controlled heat input, and post-weld heat treatment represents a holistic approach to cladding process design that addresses the multiple failure mechanisms that can affect casting roll overlays.
Study Insights and Implications
This work demonstrates the power of process innovation in solving long-standing industrial problems. The novel cladding process for continuous casting rolls is not merely an incremental improvement but a systematic rethinking of the cladding process parameters and sequence to achieve superior performance. The key insight is that the microstructure of the overlay layer, which governs its thermal fatigue and wear resistance, is determined by the cooling rate and thermal history during cladding, and that careful control of these parameters through multi-pass welding and post-weld heat treatment can yield significant performance improvements. For engineers working in the field of roll manufacturing and repair, this study provides a practical framework for optimizing cladding processes based on a thorough understanding of the metallurgical fundamentals. The work also highlights the importance of NDT and quality control in ensuring the reliability of cladded components, reinforcing the principle that process control and inspection are as critical as material selection in achieving dependable engineering performance.